Various aircraft using static lift (i.e., buoyancy) or active lift (such as that provided by airfoils) are known in the art. Lighter-than-air aircraft include balloons and airships, which use static lift for all or much of their lifting capacity. Heavier-than-air aircraft include airplanes and helicopters, both of which use active lift provided by airfoils (including rotors having lifting properties). Airfoils are configured to generate lift when air passes around the airfoil surfaces.
Another air vehicle (of sorts) is the parachute, which is used to slow the descent of (and in some cases to maneuver) a dropped object. Parachutes can have some maneuverability, but the maneuverability is generally limited.
In the 1960s, the parafoil was invented, which combined elements of both airfoils and parachutes. The parafoil is an airfoil formed from parachute-like material (e.g., nylon) configured into multiple cells that form an aerodynamic airfoil shape when inflated by oncoming airflow. U.S. Pat. No. 3,285,546 to Jalbert, which issued on Nov. 15, 1966 (the entire contents of which are hereby incorporated by reference) describes the general construction and operation of parafoils.
Parafoils are generally shapeless until inflated. Inflation occurs through ram air scoops at the leading edge of the parafoil, which channel oncoming air into the parafoil to inflate the individual cells. Inflation of the individual cells forms the desired airfoil shape. In flight, the payload of a parafoil acts as a flying pendulum, the rocking of which will generally self-correct the angle of attack of the parafoil. Parafoils generally fly straight and with a standard glide unless propulsive forces or wing warping are imparted.
Parafoils can be used with a propulsion source (such as propellers) to form a powered aircraft, and are also widely used as kites and parachutes (including spacecraft recovery). An unpowered parafoil was used as part of the recovery system of the X-38 International Space Station Emergency Crew Recovery Vehicle, the tests of which included airfoil deployment (including airfoil inflation) at an altitude of approximately 120,000 feet. At such an altitude on Earth, the air pressure is comparable to that on the surface of Mars.
Airships were developed before the advent of heavier-than-air flight, and have continued in operation to the present day. The most widely used type of airship today is the blimp, which is a non-rigid airship having a generally flexible balloon envelope filled with a lighter-than-air gas such as helium. Inside the balloon envelope are one or more ballonets that can be filled with outside air. The filling of the ballonets compresses against and displaces the helium within the balloon envelope, and as the ballonets are filled (using outside air instead of the lighter helium), the overall weight of the blimp increases. Allowing the ballonets to deflate permits the helium to expand to fill more of the envelope, thus lightening the weight of the blimp.
Blimps are generally elongated in shape and derive little or no aerodynamic lift from their overall shape, instead relying almost exclusively upon their lighter-than-air characteristics and/or propulsion systems for lift. Blimps can also have control issues when compared to airfoils.
There have been attempts to combine characteristics of airships with those of heavier-than-air ships and airfoils. For example, U.S. Pat. No. 5,005,783, which issued to James D. Taylor on Apr. 9, 1991 and is entitled “Variable Geometry Airship,” describes an airplane having an inflatable blimp-like envelope that can transition from a blimp-like configuration (making the aircraft a lighter-than-air vehicle) to a wing-like configuration (making the aircraft a heavier-than-air vehicle). Other inventors have attempted to develop aircraft having more streamlined blimp envelopes.
Although the prior art includes various configurations of aircraft, including lighter-than-air and heavier-than-air vehicles, what is needed is an aircraft of relatively simple construction configured for lighter-than-air flight but which also takes advantage of aerodynamic lifting forces, and which can be applicable to interplanetary missions and other applications involving relatively low atmospheric pressures. The current invention meets this need.